Liner for grinding mills

ABSTRACT

Liners for grinding mills having alternating bars of alloy steel and strips of an elastomer, such as rubber, bonded together and to a backing plate which is sufficiently flexible that the liner may be manufactured flat, but drawn against an arcuate portion of the cylindrical side wall of the mill by attaching bolts. Converging slots formed in the center bar of the liner are engaged by bolt heads having converging sides. For a ball mill, the bars of each liner are of the same height and the strips are of the same height, with the bars initially slightly higher than the strips. The liners are installed so that the bars and strips extend longitudinally of the mill, the effect of the balls and material being ground being to produce a corrugated or ripple wave surface on each liner which provides a lifting effect to the grinding media and causes the balls to bounce or oscillate. For rod mills, each liner has several center bars and strips of a greater height, with a series of one bar and one strip of successively lesser heights on each side of the center bars and strips. Wear during use produces not only a ripple wave contour of the bars and strips but also a higher portion of the liner toward the direction of rotation from the initial highest portion, which accentuates the lifting effect on the grinding media. A liner for a segment of the end wall of the mill includes alternating bars and strips of alloy steel and rubber, with the center bar being disposed along a radius of the end wall and the remaining bars and strips parallel thereto.

Norman LINER FOR GRINDING MILLS Teller E. Norman, 37 Hillside Dr.,Denver, Colo. 80215 [22] Filed: Sept. 11, 1972 [21] Appl. No.: 287,779

[76] Inventor:

1521 Us. c1. 241/182, 241/300 [51] Int. Cl. 1302c 17/22 [58] a Field ofSearch 241/294, 295, 298,299, 241/300, 182, 183, DIG. 30

[56] References Cited UNITED STATES PATENTS 3,194,506 7/1965 Bourne eta1. 241/300 3,533,570 10/1970 Bernutatm; 241/300 X 2,476,505 7/1949Mclntyren"; '241/182 3,378,209 4/1968 Crocheron.... 241/183 X 1,921,6728/1933 Haushalter.... 241/183 1,631,971 Y 6/1927 Linhard 241/183 FOREIGNPATENTS OR APPLICATIONS 999,521 7/1965 Great Britain 241/183 399,990 8/1924 Germany 241/182 OTHER PUBLICATIONS No. 178,351 Lining for Tube MillsThe Canadian Patent Office Record, Vol. 45, July, 1917, Page 2,180.

7 Primary Examiner-Granville Y. Custer, Jr.

Attorney, Agent, or Firm-HoraceB. Van Valkenburgh; Frank C. Lowe 1451Apr. 16, 1974 [5 7] ABSTRACT Liners for grinding mills havingalternating bars of alloy steel and strips of an elastomer, such asrubber, bonded together and to a backing plate which is sufficientlyflexible that the liner may be manufactured flat, but drawn against anarcuate portion of the cylindrical side wall of the mill by attachingbolts. Converging slots formed in the center bar of the liner areengaged by bolt heads having converging sides. For a ball mill, the barsof each liner'are of the same height and the strips are of the sameheight, with the bars initially slightly higher than the strips. Theliners are installed so that the bars and strips extend longitudinallyof the mill, the effect of the balls and material being ground being toproduce a corrugated or ripple wave surface on each liner which providesa lifting effect to the grinding media and causes the balls to bounceoroscillate. For rod mills, each liner has several center bars and stripsof a greater height, with a series of one bar and one strip ofsuccessively lesser heights on each side of the center bars and strips.Wear during use produces not only a ripple wave contour of the bars andstrips but also a higher portion of the liner toward the direction ofrotation from the initial highest portion, which accentuates thelifting: effect on the grinding media. A liner for a segment of the endwall of the mill includes alternating bars and strips of alloy steel andrubber, with the center bar being disposed along a radius of the endwall and the remaining bars and strips parallel thereto.

10 Claims, 14 Drawing Figures 1 LINER FOR GRINDING MILLS This inventionrelates to liners for grinding mills, such as ball mills and roclmillsused in grinding or comminuting ore and the like.

Grindingmills are used for the purpose of reducing the size of lumps orother pieces of ore or the like for various purposes. In the case ofore, the normal function of the grinding mill is to reduce the size ofthe ore to particles within a fine sieve range for flotation, in whichthrough the use of suitable additives, the ore bearing particles areseparated from the gangue. Both ball mills and rod mills have been usedfor grinding ores or the like, such a mill normally being a rotatingcylinder containing a number of balls or rods formed of steel, usuallyspecial alloy steels, which crush and comminute the ore between them oragainst the side of the mill, or perhaps the end thereof. In addition toballs or rods, pebbles or natural rock have also been used as grindingmedia. A grinding mill thus normally consists of a cylindrical shellrotated about a-central horizontal axis, with ends which close theendsof the shell. Various diameters and lengths of shells have beenutilized, varying considerably but normally in proportion to thecapacity of the mill. In view of the abrasive character of the materialbeing ground, the wear on the inside of a grinding mill has been aserious problem. Normally, grinding mills have been lined with cast orwrought abrasion resistant ferrous alloy liners several inches thick, orin some cases, with rubber or ceramic liners. These liners have beenmade in sections, with various configurations, usually being held inplace by bolts which hold the liner tightly against the interior of the1 mill shell or the mill end. Cast ferrous alloy liners require moldsfor the production thereof, while liners manufactured from wrought steelrequire special rolls for forming to shape. a

During service; the liners tend to be worn easily by the abrasive actionof the grinding media and the minerals being ground in the mill. Thecost of periodic re- 1 placementof liners is thus a major item of costin the operation of mills or plants which'grind ore or other minerals.ln'addition, the configuration of thesurface' of the liner, during itsservice life, has been found to be an importantconsideration affectingboth the life of the' liner and the grinding efficiency or grinding rateof the mill. Furthermore, a configuration which produces the highestgrinding efficiency or grinding rate for a ball mill is not necessarilythe configuration which will produce the highest efficiency or grindingrate for a rod mill, and vice versa. j

Among the objects of this invention are to provide a .novel liner forgrinding mills; to provide such a liner which may be adapted for use asa liner for the shell and also aliner for an end of the mill; to providesuch a liner which has a longer life and therefore requires replacementat less frequent intervals; to provide such a liner which is'readilymodified in construction, to provide a configuration most suitable foruse in a ball mill or pebble mill, as well as a different configurationwhich is most suitable for use in a rod mill or an autogenous grindingmill using large diameter natural rock; to provide such a liner whichmay be readily manufactured in a flat or planar form but will fittightly against the mill shell, irrespective of the'mill diameter,thereby avoiding the cost of machining or of molds for casting linersfor shells of different diameters; to provide such liners which may bemade in different lengths and widths without undue expense; to providesuch liners which may be modified for use in grinding fine or softmaterials; and to provide such liners which are economical tomanufacture and are efficient and effective in use.

The foregoing objects are generally accomplished by utilizing a seriesof longitudinally extending, alternating strips of highly abrasionresistant material, such as hardened alloy steel, and strips ofelastomer, such as rubber, which are bonded to each other and to abacking plate, to form a laminated composite liner. The backing plate,as of soft steel or the like, will conform to the inner diameter of theshell when attached thereto, while the resiliency of the elastomerstrips permits compression thereof toaccommodate the curvature of theshell. For use in ball mills or pebble mills, the height of the morehighly abrasion resistant strips or bars is slightly greater than theheight of the alternating elastomer strips, in order to provide what maybe characterized as a low wave ripple configuration. For rod mills orautogenous grinding mills, with large diameter natural rock as grindingmedia, the height of the strips and bars 'are varied to provide agreater height at the center of theliner, to produce what may becharacterized as a high wave" ripple configuration. For lining the endsofa cylindrical mill, the low wave configuration is convenientlyutilized, with the bars and stripsextending radially of each liner,which forms a segment of the circle of the end of the mill. When fine orsoft materials are ground, a good quality of abrasion resistant rubberor other elastomer may prove to have a greater abrasion resistance thansteel or iron. In this case, higher bars should be made fromthe abrasionresistant rubber or other elastomer and the lesser abrasion resistantstrips may be made of other suitable material, such as a harder, lessabrasion resistant rubber or elastomer, a suitable plastic material orhard wood.

The attainment of the foregoing. and additional objects of thisinvention, as well asthe novel features thereof, will further beapparent from the following description of preferred embodiments of thisinvention, illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view, on a reduced scale, of

a grinding mill in which the liner of this invention is particularlyuseful;

FIG. 2 is a fragmentary circumferential section, showing one segmentalliner constructed in accordance with this invention, portions of twoadjacent liners and a portion of the shell of the grinding mill in whichthe liners areinstalled, such liners being particularly useful for aball mill;

FIG. 3 is a fragmentary section, on an enlarged scale,

I taken along line 3-3 of FIG. 2 and showing particularly the head of aninstallation bolt and associated parts;

FIG. 4 is a fragmentary section taken along line 4----4 of FIG. 3;

FIG. 5 is a fragmentary section, similar to FIG. 2 but showing thecondition of the alternating steel and elastomer strips after wear towhat may be characterized as a low, wave" configuration;

FIG. 6 is a transverse section of the of FIG. 2, prior to installation;

FIG. 7 is a. condensed top plan view of the liner of FIG. 6;

grinding mill liner FIG. 8 is a fragmentary section, similar to FIG. 2but FIG. 9 is a fragmentary section, on an enlarged scale and takenalong line 9-9 of FIG. 8;

FIG. 10 .is a fragmentary section, taken along line 10-10 of FIG. 9;

FIG. 1 1 is a fragmentary section, similar to F IG. 8 but showing theliner segment after wear to what may be characterized as a high waveconfiguration;

FIG. 12 is a transverse section of the grinding mill liner of FIG. 8,prior to installation;

FIG. 13 is an inside view of one end ofa grinding mill, also providedwith liners constructed in accordance with this invention, the shell andshell liners being omitted for clarity of illustration; and

FIG. 14 is a planar section, on an enlarged scale, of one of the linersof FIG. 13.

A rotating cylindrical grinding mill, ofa type in which linersconstructed in accordance with this invention may be used, is shown inFIG. 1 and includes a cylindrical shell 10 having bolts 11 by which theliners are attached to the inside of the shell, with the bolts extendingtherethrough. An end plate 12 is attached to one end of the shell 10 anda corresponding end plate is attached to the opposite end of the shell,while a cover 13 for a ring gear 14, having teeth (not shown), enclosedwithin the cover 13 is disposed at one end of the mill. The ring gear isengaged by a gear drive, which is conventional and therefore not shown.The grinding mill is mounted for rotation through bearings 15 and 16 atopposite ends of the mill, with supports 17 and 18 for the respectivebearing being mounted on any suitable type of foundation. The ore orother material to be ground is introduced into the mill through a feedtube 19, while the ground material is discharged from the mill through adischarge tube 20, as indicated by the arrows.

A liner L, constructed in accordance with this invention and illustratedin FIG. 2, is flanked by portions of additional liner sections Lconstructed in the same manner, all mounted on the inside of the shell10 by bolts 11. Each liner L may cover a section of the circumference ofthe shell 10, with each liner or two or more liners placed end to endcorresponding to the length of the shell so that the length of eachliner L may be such that the weight thereof permits it to be relativelyeasy to handle. For a mill shell which has a 10 footinside diameter,there may be 20 rows of liners, each occupying an 18 segment of theshell. Thus, the chord width of an l8 segment for a 10 foot insidediameter shell would be 18.84 inches. However, a clearance or space 21between adjacent liners is desirable, so that the liner L, in theinstance under discussion, may be l8-5/l 6 inches wide. When more thanone liner is placed end to end in the shell, a spacing between the endsof these two liners, similar to the spacing between adjacent liners, maybe provided.

The liner L includes a series of hardened alloy steel bars 22 whichalternate with a series of elastomer strips 23, such as formed ofrubber, of the same width and length, and a pair of outside elastomerstrips 23 of lesser width, for the liner illustrated. The alternatingbars 22 and strips 23 may have a similar width, such as between inch and2 inches, with the bars 22 and strips 23, as shown inFIG. 2, beingapproximately l-5/l6 inches in width and the outside elastomer strips 23being inch in width. The upper ends of the steel bars 22, which may berounded as shown, are spaced above the elastomer strips 23 a distanceless than the width of the steel bars, such as approximately h inch,when the bars and strips have the dimensions indicated above. Of course,for other widths of bars and strips, or for a liner made for a grindingmill shell having a different diameter, the outside strips 23' may beunnecessary.

In accordance with this invention, each of the bars 22 and strips 23 and23' are bonded to each other and to a backing plate 24, which may beformed of a low carbon steel, since it is not subjected to abrasionduring use. A rubber strip 25 is conveniently disposed between thebacking plate 24 and the bars and strips, for bonding purposes. Thus,the steel bars 22 and elastomer strips 23 and 23' may be bonded to eachother and the backing plate 24, through the strip 25, by a suitablerubber cement mixture, followed by vulcanization, as in an autoclave, toproduce a strong bond. Other suitable ways of attaching the bars 22 andstrips 23 to each other and to the backing plate 24 may, of course, beutilized. The thickness of backing plate 24 need not be great, so that,when the liner is mounted against the inside of the shell 10 by a seriesof bolts 11, as in FIG. 2, the backing plate 24 will bend to conform tothe inside of the shell. It will be noted that the liner L is initiallyformed in a straight or planar condition, as in FIG. 6, and that thebacking plate 24 will be curved, when the backing plate is drawn intoengagement with the inside of the shell, as in FIG. 2. The elasticity ofthe strips 23 will permit a slight compression, principally along theupper portion thereof, by the steel bars 22, when the liner isinstalled. Thus, there should be no difficulty in the liner conformingto the inside curvature of the shell 10, substantially irrespective ofthe diameter thereof.

For bolt attachment purposes, a series of slots 27, as in FIG. 7,corresponding to the number of bolts 11 utilized in attaching the linerto the shell, are provided between sections of center bar 22. Each slot27 has a rectangular configuration down to an angular surface 28 at eachside and which slants inwardly toward a hole 29 in the backing plate 24,when installed, is in alignment with a hole 32 in shell 10, throughwhich the shank of a bolt 11 extends. Each bolt head 30, as in FIGS. 3and 4, is generally rectangular in cross section down to opposed angularsurfaces 31 which fit against the corresponding angular surface 28 ofthe corresponding slot 27, to permit the bolt to draw the liner tightlyagainst the shell 10. The shell 10, in appropriate positions, isprovided with a series of holes 32 through which the shank of each bolt11 extends, as for attachment of a conventional washer and nut, as inFIG. 2.

Since the direction of impingement of the grinding media and theminerals on the liners is approximately perpendicular to the joint linesbetween the laminated bars and strips, the action of the grinding mediaand minerals tends to produce different rates of wear on the moreabrasion resistant bars and less abrasion resistant strips,respectively. Thus, as the liner wears, it developes a ripple wavewearing surface, as shown in FIG. 5. This ripple wave or corrugatedcontour persists on the liner surface until it is worn down to. thesteel backing plate. At that time, the worn liners may be replaced witha new set of liners. The ripple wave contour pro.- vides the desiredlifting effect to the charge of grinding media, as the mill rotates, andalso causes the balls to surface of a liner, as when each liner isformed from one material. As will be evident, the use of the linerconstruction of this invention reduces the wear of the liner andtherefore increases its useful life, as compared with the types ofliners used herefore.

As indicated previously, the alternating bars and strips, with the moreabrasion resistant bars slightly higher than the less abrasion resistantstrips, but with all of the bars normally of about the same height andall of the strips normally of about the same height, provides the lowwave configuration illustrated in FIG. 5. As indicated previously, thislow wave configuration is particularly useful for ball mills and pebblemills.

For rod mills, i.e. mills in which elongated rods are placed in themill, rather than balls, or mills using an autogenous grinding media ofrelatively large diameter or sized rocks of the material being ground,the high wave" configuration shown in FIG. 11, produced by theconfiguration of FIG. 8, as it wears, is particularly useful. As in FIG.8, a high wave liner L will include a pair of longitudinally abuttingcenter bars 35 of alloy steel provided with bolt slots 27', with anotherpair of bars 36 outside the center bars, but with elastomer strips 37interposed therebetween. The central bars 35, 36 and strips 37 are thehighest of the bars or strips utilized in this embodiment, for a purposedescribed later. On each side of the center bars 36 is an elastomerstrip 38 and then a hardened alloy steel bar 39, each of lesser heightthan the central bars and strips; then strips 40 and bars 41 of lesserheight and strips 42 and bars 43 of successively lesser height. A pairof narrower elastomer strips 44, of the same height as bars 43, completethe assembly of bars and strips onthe outside. A space 21', betweenliners L, is provided, as before. As before, the bars and strips of theliner L are bonded together and to a backing plate 24' by a rubber strip25, as in the manner described previously. The respective liners L areattached to the interior of the shell of the mill by bolts II, with eachliner occupying a predetermined arcuate portion of the innercircumference of the shell and the liners having either a lengthcorresponding to the shell, or two or three liners placed end to endlongitudinally of the shells, for shells with increasing longitudinaldimensions. Slot 27' of each bolt 11 is again rectangular in crosssection to an inwardly angular surface 28' at each side but is formedbetween aligned sections of the two center bars 35, rather than betweensections of a single bar. Head 30' of bolt 11' is similar inconfiguration to the bolt heads 30 of FIG. 3, except for the height,being provided with a longer angular surface 31' adjacent the shank ofthe bolt, with the angular surfaces of the bolts being longer than theangular surfaces 30 of the bolt 11, to compensate for the greater weightof the liner of the "high wave configuration. For the high wave"configuration, the center bars 35, strips 37 and bars 36 may be on theorder of 6 inches high, with the strips 38 and bars 39 being the orderof inch and V2 inch wide, or a total width of 18% inches. The width ofthe liners may, of course, vary considerably, such as ranging from about15 inches to about 24 inches in width.

During the use of liners L' of FIG. 8, when rotated in the direction ofthe arrow 45 of FIG. 11, the impingement of the grinding media andmaterial being ground, on the bars andstrips, will tend to wear away toa greater extent the bars 35 and strips 37, as well as the bars andstrips on the side opposite the direction of rotation, so that thegenerally higher portion of the liner will become the bars and stripsdisposed toward the direction of rotation. Such wear will produce apronounced peak, as well as a series of peaks and valleys of a generallylesser height. However, the differential effect of the differences inheight of the portions of the liner toward and away from the directionof rotation will accentuate the lifting effect on the rods in the rodmill, or large diameter rock utilized in an autogenous grinding mill.

For lining either end of the mill, such as end 12 of FIG. I or theopposite endof the grinding mill, the low wave ripple configuration ispreferable. Thus, each end of the grinding mill may be provided with aseries of liners L", each corresponding to a segment of the annulusbetween the inner circle 50 and outer circle 51 of the grinding millend. Spaces 52 may be provided between the liners L, similar to thespaces 21 of FIG. 2 and 21' of FIG. 8. Each liner L" or segment may havethe construction illustrated in FIG. 14, such as including a center bar53 formed of hardened alloy steel and a pair of elastomer strips 54 oneach side thereof and disposed parallel thereto. It will be noted thatthe center bar 53 extends radially of the end of the mill. Additionalbars 55, 56 and 57 may also extend parallel to the center bar 53,interspersed with elastomer strips 58, 59 and 60 of the same ordifferent width, and again extending parallel to the center bar. Thebars and strips of FIGS. 13 and 14 have relative heights similar to thebars and strips of FIG. 2. During use, the alternating bars and stripswill tend to become worn to a low wave ripple configuration, similar tothat shown in FIG. 5. The center bar 53 is provided with bolt slots 27between sections, similar to the bolt slots 26 of FIG. 3 and adapted toreceive the boltsfor attaching the liner L" to the end plate,such as theend plate 12 of FIG. 1, or the opposite end plate. With respect to theliner L, it will be noted that these liners are not only manufactured ina flat form, but also utilized in a flat form, or they may deform whenbolted in the mill to fit the slightly conical surface which exists atthe ends of many grinding mills. As before, the alternating strips andbars are bonded to each other and may be bonded to asuitable backingplate corresponding to backing plate 24 of FIG. 6, with a rubber stripinterposed between the backing plate and the alternating bars and stripsto fa- 'cilitate bonding, as in the manner described, through a rubbercement mix and vulcanizing.

The advantages of the liners of grinding mills constructed in accordancewith this invention are numerous. Thus, the liners of this inventionhave a longer life, primarily due to the ripple wave contour whichpersists throughout the life of the liner. A contributing factor is thatunusually hard and abrasion resistant metal bars can be used in theconstruction of these liners, since each bar is well supported by andsecurely bonded to the tough rubber bars and to the mild steel backingplate, so that even if a metal bar cracks in service, it willcontinue tobe held in place and perform its desired function throughout the life ofthe liner. Thus, the liners can be worn down to a very thin sectionbefore replacement is necessary. The liners of this invention also havea lower first cost than homogeneous liners of equivalent volume orthickness, due to the fact that the metal bars can be made from standardand relatively light sections, either rolled or cast, which can beproduced at a lower cost per unit weight than the special heaviersections required in homogeneous cast or rolled liners. The alloyingelements needed for the lighter section bars to produce full hardeningis also less than for heavy sections. The rubber or elastomer strips inthe composite liner can also be produced at a sub- Y stantially lowercost per unit volume than a homogeneous metal liner of heavysection. Formaking up composite liners, it is desirable to use only a few sizes orpreferably one size of steel bars in a standard and therefore readilyavailable dimension. If necessary, a greater number of sizes of rubberbars may be used to provide the desired width of the liner. The lengthof the individual bars, as supplied to the shop, can be variable, sincethey can be cut or trimmed at the shop to a desired length. Cuts on theends of the sections of the bars which abut the bolts can be madeaccurately with an abrasive cut off wheel, or by any other suitablemeans available for cutting hardened tool steel. While there is anadditional assembly cost involved in the production of composite ripplewave" liners, this cost is relatively low and is only a small fractionof the cost of materials.

The liners of this invention produce an increased grinding rate in themill, due to the fact that the grinding media are activatedandoscillated by the ripple wave" effect. When desired, relatively thinliners may be used to increase the effective interior diameter of thegrinding mill.

The liners of this invention require less shut down time of the mill forliner changes, due to the inherently longer life of the liners and alsoto their ease of handling. If desired, the number of pieces to behandled can be reduced by the use of longer liners, which lendthemselveswell to production in the ripple wave" configuration.

It will be understood that the method or design of bolt attachment maybe changed from the forms shown. For instance, a series of cap screwsextending through the wall of the mill may be utilized to attach eachliner to the inside of the mill. In such an instance, it may bedesirable to use a softer steel strip, such as S.A.E. 1040, which ismore readily tapped, for anchoring the cap screws. Such a softer steelstrip may be flanked by thin strips of rubber or the like and hardersteel bars on each side thereof. Such a construction avoids cutting thesofter steel strip and also eliminates the hole or socket at each bolthead.

Although certain preferred embodiments of this invention have beenillustrated and described, it will be understood that other embodimentsmay exist and that various changes may also be made, such as in methodsor designs of bolt attachment, or in widths of the indi- 8 vidual barsand strips forming the laminated composite, without departing from thespirit and scope of this invention.

What is claimed is:

l. A liner for at least a portion of the interior of a grinding milladapted to utilize iron balls, steel balls, iron rods, steel rods,pebbles, rocks and the like as the grinding media, comprising:

bars formed of a relatively high abrasion resistant material;

strips formed of less abrasion resistant material and alternating withsaid bars; and

means for maintaining said bars and strips in alternating relation,whereby when installed in said mill, said bars and strips will engagethe material to be ground and will wear differentially to produce acorrugated or ripple wave surface contour.

2. A liner as defined in claim 1, wherein:

said bars have the abrasion resistant qualities of alloy steel; and

said strips are formed of an elastomer having substantially the abrasionresistant qualities of rubber.

3. A liner as defined in claim 1, wherein:

said bars are formed of an elastomer having the abrasion resistantqualities of rubber; and

said strips are formed of a less abrasion resistant material.

4. A liner as defined in claim 2, including:

a backing plate extending beneath said bars and strips, said bars andstrips being bonded to each other and to said backing plate.

5. A liner as defined in claim 4, wherein:

said backing plate is sufficiently flexible to permit said backing plateto be manufactured with said backing plate flat, but said backing plateconforming to an arcuate portion of a cylindrical side wall of saidgrinding mill when installed with said bars and strips extendinglongitudinally of said mill through the compression of said elastomerstrips.

6. A liner as defined in claim 1, wherein:

said liner has a configuration conforming to a segment of an end wall ofsaid mill, with a center bar or strip extending in a directioncorresponding to a radius of said end wall and the remaining bars andstrips generally parallel to said center bar or strip.

7. In a liner as defined in claim 1, wherein:

each of said bars is initially of substantially the same height; and

each of said strips is initially of substantially the same height.

8. A liner as defined in claim 1, including:

a series of centrally disposed bars and strips of a predeterminedheight; and

a plurality of series of at least one bar and one strip disposedlaterally at each side of said centrally disposed bars and strips, witheach series having a successively lesser height.

9. A liner as defined in claim 1, wherein:

the composite assembly has sufficient lateral elasticity to permit it tobe manufactured with a flat back but said flat back will conform to anarcuate portion of a side wall of said mill, with said bars and stripsextending longitudinally of said mill.

10. A liner as defined in claim 1, for installation on a cylindricalside wall of a mill, wherein:

10 with converging side surfaces to engage the converging side portionsof the corresponding slots, whereby the bars may extend longitudinallyof said mill.

1. A liner for at least a portion of the interior of a grinding milladapted to utilize iron balls, steel balls, iron rods, steel rods,pebbles, rocks and the like as the grinding media, comprising: barsformed of a relatively high abrasion resistAnt material; strips formedof less abrasion resistant material and alternating with said bars; andmeans for maintaining said bars and strips in alternating relation,whereby when installed in said mill, said bars and strips will engagethe material to be ground and will wear differentially to produce acorrugated or ripple wave surface contour.
 2. A liner as defined inclaim 1, wherein: said bars have the abrasion resistant qualities ofalloy steel; and said strips are formed of an elastomer havingsubstantially the abrasion resistant qualities of rubber.
 3. A liner asdefined in claim 1, wherein: said bars are formed of an elastomer havingthe abrasion resistant qualities of rubber; and said strips are formedof a less abrasion resistant material.
 4. A liner as defined in claim 2,including: a backing plate extending beneath said bars and strips, saidbars and strips being bonded to each other and to said backing plate. 5.A liner as defined in claim 4, wherein: said backing plate issufficiently flexible to permit said backing plate to be manufacturedwith said backing plate flat, but said backing plate conforming to anarcuate portion of a cylindrical side wall of said grinding mill wheninstalled with said bars and strips extending longitudinally of saidmill through the compression of said elastomer strips.
 6. A liner asdefined in claim 1, wherein: said liner has a configuration conformingto a segment of an end wall of said mill, with a center bar or stripextending in a direction corresponding to a radius of said end wall andthe remaining bars and strips generally parallel to said center bar orstrip.
 7. In a liner as defined in claim 1, wherein: each of said barsis initially of substantially the same height; and each of said stripsis initially of substantially the same height.
 8. A liner as defined inclaim 1, including: a series of centrally disposed bars and strips of apredetermined height; and a plurality of series of at least one bar andone strip disposed laterally at each side of said centrally disposedbars and strips, with each series having a successively lesser height.9. A liner as defined in claim 1, wherein: the composite assembly hassufficient lateral elasticity to permit it to be manufactured with aflat back but said flat back will conform to an arcuate portion of aside wall of said mill, with said bars and strips extendinglongitudinally of said mill.
 10. A liner as defined in claim 1, forinstallation on a cylindrical side wall of a mill, wherein: a centralbar of said liner is divided into sections, with the ends of adjacentsections formed to provide a slot, at least a portion of the sides ofwhich converge toward said side wall; and a series of bolts forattaching said liners to said side wall of said mill, said bolts havingheads provided with converging side surfaces to engage the convergingside portions of the corresponding slots, whereby the bars may extendlongitudinally of said mill.